Standards, methods for making, and methods for using the standards in evaluation of oxide removal

ABSTRACT

An article of manufacture forms a tool for determining cleaning parameters of an oxide removal process. The article comprises a block of material upon which an oxide can be formed and a simulated defect structure disposed in the block of material. The article is capable of determining oxide removal parameters of an oxide removal process by disposing an oxidized standard in a reactor, conducting an oxide removal process to remove oxide from the standard, and evaluating the standard and simulated defect structure for remaining oxide and other oxide removal parameters.

BACKGROUND OF THE INVENTION

[0001] The invention relates to standards for evaluating oxide removal,methods of making the standards, and their associated methods of use.

[0002] Aeronautical, marine, and land-based turbine components, such as,but not limited to, blades, shrouds, and vanes, are exposed tohigh-temperature oxidizing, and often corrosive, environments duringservice. Surfaces of turbine components, including cracks, may formcomplex, chemically stable thermal oxides during use. These oxidescomprise, but are not limited to, oxides of aluminum, titanium,chromium, and combinations thereof.

[0003] Turbine components are periodically overhauled in order toprolong life or enhance performance. During these overhauls, the turbinecomponents may be subjected to various repair operations, includingwelding, brazing, or coating. The presence of stable oxides impairs thereparability of a superalloy. Therefore, removal of these oxides priorto repair, for example by cleaning the turbine components, is importantfor successful turbine overhaul.

[0004] Grit-blasting or grinding operations can effectively removesurface oxides when only superficial repairs are required and thesurfaces to be cleaned are readily accessible. These cleaningoperations, however, are not only labor intensive but can result ininadvertent and undesirable loss of the base alloy material, thuscompromising the turbine component's reliability and efficiency.Further, repair of hard-to-reach surfaces, including internal passagesand highly concave sections, such as, but not limited to, cooling holes,cracks, and slots, generally requires a non-mechanical cleaning processthat minimally degrades or consumes the base alloy. These cleaningprocesses have included batch thermo-chemical cleaning, such asprocesses that occur in a high-temperature reactive environment. Thesebatch turbine-component cleaning processes can, in some cases, rely onfluoride ions, which are provided in a reactor to remove highly stableoxides from, cooling holes, cracks, slots, and other hard-to-reachsurfaces. The fluoride-ion cleaning (FIC) processes are known to removeoxides while leaving the turbine component's base alloy essentiallyintact.

[0005] While processes such as FIC are useful for cleaning oxides onturbine components, the process effectiveness, especially with respectto oxide removal from, cooling holes, cracks, slots, and otherhard-to-reach surfaces, is difficult to quantify. Known measures ofoxide removal comprise sectioning of cleaned turbine components andmeasuring the extent of oxide cleaning. This measure does not provide aconsistent indication of overall oxide removal, since both the damageand oxidation characteristics of each turbine component will vary.Therefore, a tool that can consistently gauge the effectiveness of anoxide removal process would be desirable.

SUMMARY OF THE INVENTION

[0006] The invention sets forth an article of manufacture comprising ablock of material upon which an oxide can be formed and a defectstructure disposed in the block of material. The article is capable ofbeing used to assess the effectiveness of an oxide removal process bymeasuring oxide removal from the block and defect structure aftersubjecting it to an oxide removal process.

[0007] The invention further sets forth a tool for determining oxideremoval parameters of an oxide removal process. The tool comprises ablock of material upon which an oxide can be formed and a defectstructure disposed in the block of material. The tool is capable ofbeing used to assess the effectiveness of an oxide removal process bymeasuring oxide removal from the block and defect structure aftersubjecting it to an oxide removal process.

[0008] Another embodiment of the invention provides a process fordetermining an oxide removal effectiveness. The process comprisesdisposing an oxidized standard in a reactor that is capable of oxideremoval. The standard comprises a block of material upon which an oxidecan be formed and a defect structure disposed in the block of material.The method further includes conducting an oxide cleaning and evaluatingthe standard for remaining oxide.

[0009] A further embodiment of the invention comprises a process forforming an oxide removal evaluation standard. The standard comprises ablock of material upon which an oxide can be formed and a defectstructure disposed in the block of material. The process comprisesmachining the slot structure in the block of material, compressing thedefect structure to form at least one crack-like defect, and exposingthe block of material to a thermal treatment to form an oxide on theblock surfaces and within the at least one crack-like defect.

[0010] These and other aspects, advantages and salient features of theinvention will become apparent from the following detailed description,which, when taken in conjunction with the annexed drawings, where likeparts are designated by like reference characters throughout thedrawings, disclose embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011]FIG. 1 is a schematic illustration of a standard for evaluatingeffectiveness of oxide removal processes;

[0012]FIG. 2 is a flow chart of a method for making and using standards,as embodied by the invention, and for evaluating effectiveness of oxideremoval processes; and

[0013]FIG. 3 is a schematic illustration of a second standard forevaluating effectiveness of oxide removal processes.

DETAILED DESCRIPTION OF THE INVENTION

[0014] Oxide removal from engine-run turbine components is an importantstep in turbine component repair and overhaul processes. The inventionprovides a tool for evaluating performance of oxide removal processes.The tool is useful in quantifying oxide removal from cracks and otherhard-to-reach surfaces, including cooling holes, slots, internalpassages, and other highly concave sections (hereinafter referred to as“defects”).

[0015] The tool, as embodied by the invention, comprises a standardspecimen that enables the extent and effectiveness of oxide removal tobe evaluated. The standard comprises a solid article, for example anarticle having a generally rectangular-solid geometry. The standardtypically comprises a material similar to that which is to be cleaned.For example, and in no way limiting of the invention, if an oxideremoval process is used in repair of turbine components that are formedof superalloy materials, the standard is formed from a similarsuperalloy material, such as nickel-, cobalt-, or iron-basedsuperalloys, or combinations thereof.

[0016] One embodiment of a standard 1 will be described, along withmethods of its formation and use, with reference to FIGS. 1 and 2 andthe flowchart of FIG. 3. The following structure is merely exemplary ofstandards within the scope of the invention, and is not meant to limitthe invention in any way. The standard 1 comprises a solid block 2(hereinafter “block”), for example a block formed of a superalloymaterial. The scope of the invention includes forming the block 2 in anyappropriate shape, including but not limited to, a general rectangularsolid. The block 2 may also comprise protrusions and depressions formedthereon. The following description of the invention will refer to agenerally rectangular block, however this is merely exemplary and is notmeant to limit the invention in any way.

[0017] The block 2 includes a defect structure. The defect structurecomprises at least one slot 3 on surface 4 and the block 2 comprises anotch 5. As illustrated in FIG. 1, the notch 5 comprises a “V”(“Chevron”) notch 5 on an opposite surface 6, and having its apex 13substantially co-linear with the slot 3. This configuration of a notch 5is merely exemplary of notches within the scope of the invention. Thescope of the invention comprises notches of varying sizes, shapes, andconfigurations, for example and in no way limiting of the invention,rectangular, curved, and combinations thereof.

[0018] The slot 3 comprises a thickness “t”, for example a constantthickness “t” in a range from about 10 micrometers (elm) to about 1millimeter (mm), and a length in a range from about 1 mm to about 10 mm.The slot 3 and “V” notch 5 are formed in the block 2 by an appropriateprocess, such as, but not limited to, a wire electro-discharge machining(WEDM) process, in step S1 (FIG. 3).

[0019] The depth of the “V” notch 5 is generally similar to the depth ofthe slot 3. The “V” notch 5 and slot 3 define a bridge 7 of solidmaterial in the block 2 that is disposed between the slot 3 and “V”notch 5. Typically, the height H, width W, thickness T of the standardare in a range from about 0.5 centimeter to about 10.0 centimeters. Forexample, the ratio H/T is in a range from about 0.5 to about 2.0, andthe ratio of W/H is in a range from about 0.5 to about 1.0.

[0020] After the “V” notch 5 and the slot 3 are formed in the standard1, the block 2 is cleaned in step S2 to remove any residue from theslot-structure formation processes. For example, if a machining processis used to form the slot structure, the block is cleaned to removeresidue, such as but not limited to, oils, machining chips, recast andoxide deposits, and the like.

[0021] If the slot 3 is formed with a thickness t that simulates arelevant defect thickness, no compression is needed. If the thickness“t” of the slot 3 is greater than the thickness desired for use as astandard, the slot 3 can be compressed to a more desired finalthickness. The block 2 is compressed (step S3) by applying a distributedforce on surfaces 18 and 19 in a direction indicated by arrows 10 (FIG.1). The formation of a slot structure, including any compression of theslot(s) creates a structure that simulates a defect, where defectincludes cracks, holes, crevices, and other hard-to-reach surfaces(hereinafter “simulated defect”).

[0022] After the optional compression, the block 2 is exposed to athermal treatment in step S4. An exemplary thermal treatment, which iswithin the scope of the invention, comprises, but is not limited to, asolution heat treatment followed by controlled exposure to ahigh-temperature, oxidizing environment for a time period sufficient toform oxides on both the block surface and the inside of the simulateddefect.

[0023] The standard 1, with the oxide-filled simulated defect can beused for oxide-removal process evaluation. The evaluation comprisesdisposing the oxidized standard 1 in a cleaning reactor. The scope ofthe invention comprises any cleaning reactor and any oxide removalprocess that the reactor can employ. The exact type of cleaning reactorand process used does not affect the standard per se. The standard 1 isplaced, by itself, and alternatively with other standards, in a reactor.Alternatively, the standard 1 is placed in the reactor with turbinecomponents to be cleaned. The standard 1 is then subjected to an oxideremoval process, in step S5. Once the oxide removal process is complete,the standard 1 is removed from the reactor for evaluation.

[0024] The evaluation of the standard 1 comprises exposing the simulateddefect and its surfaces in step S6. The simulated defect is exposed bycompressing the standard 1 at the “V” notch 5, in the direction ofarrows 11 (FIG. 1), thus splitting the standard 1 to open the simulateddefect.

[0025] Evaluation of the simulated defect, in step S7, can also includemetallographically sectioning the standard 1. The surfaces of theexposed slot 3 are evaluated for extent of oxide removal using various,known evaluation techniques. These evaluation techniques, include, butare not limited to, optical inspection, electrical resistivitymeasurement, weight loss measurement, and wetability evaluation.

[0026] A second embodiment of a standard 20, as embodied by theinvention, is illustrated in FIGS. 4 and 5, and its formation and useare similar to that described above with respect to FIG. 3. The standard20 comprises a block 2 of solid material. The simulated defect for thestandard 20 comprises at least one slot 21, which is formed similar toslot 3 described above. For example, the slot structure comprisesmultiple slots 21, which are machined into the block 2, for example atleast one slot in each of surfaces 24 and 26. The following descriptiondiscusses multiple slots 21, however this is merely exemplary of theinvention and is not meant to limit the invention in any way.

[0027] The standard 20 is cleaned (step S2) and, if desired, compressed(step S3) as described above to form simulated defects. The standard 20is then subjected to a heat treatment to oxidize the surface and slotstructure. The standard 20 is then oxidized (step S4), as discussedabove. The standard 20 is then disposed in a cleaning reactor, andsubjected to an oxide removal operation (step S5).

[0028] Once the oxide removal operation is complete, the standard, whichcomprises the simulated defect slot structure, is ready for evaluation.The evaluation comprises exposing the crack-like defect, such as bymetallographic sectioning, in step S6 and evaluating in step S7.

[0029] The standards 1 and 20 are evaluated for oxide removal, based onthe known starting defect. The evaluation of oxide removal provides anindication of the effectiveness of the oxide removal capabilities of theoxide removal process. For example, and in no way limiting of theinvention, performing an oxide removal process for a prescribed time ona standard having known oxide amount and in a reactor with knownoperational specifications provides oxide removal process benchmarks,which are indicative of the oxide removal process performance.

[0030] The standard can be used as an oxide-removal process guage todetermine oxide removal process progress. The standard indicates thedegree of oxide removal. For use as an oxide-removal process gauge, astandard is prepared with known oxide amounts. The standard is placed ina reactor and cleaned, as discussed above. The standard, which isdisposed in the reactor, can be checked for the degree of oxide removalagainst the oxide removal process benchmarks. Therefore, it is possibleto gauge whether a oxide removal process has removed sufficient oxideamounts for turbine components.

[0031] Either of the standard structures described above can be used toevaluate braze or welding repair effectiveness. In a braze-repaireffectiveness evaluation process, a simulated defect structure isprovided in a standard, the standard is oxidized, and then cleaned, asdescribed above in steps S1 through S5. A braze alloy is disposed on atleast some portion of the standard and may be placed over at least oneof the simulated defect structures. The standard then undergoes brazingand, if necessary, any subsequent thermal treatments, as known in theart, to form a brazed standard. The brazed standard is evaluated, asdiscussed above in step S7. For example, the brazed standard ismetallographically sectioned, inspected, and evaluated for braze-repairparameters. Exemplary braze repair parameters comprise, but are notlimited to, extent of oxide removal, depth of braze filling, andalloying element depletion. The evaluation of the brazed standardprovides an indication of the effectiveness of the brazing preparationsteps and the effectiveness of the braze repair process.

[0032] As discussed above, the standard's simulated defect structureconfiguration may vary. While the above description sets forth anelongated and planar slot, this slot configuration is merely exemplaryof slot configurations within the scope of the invention. For example,the scope of the invention comprises a simulated defect that simulatescooling hole dimensions, which is used to determine oxide removal fromcooling holes in a turbine component.

[0033] The standards, as embodied by the invention, are also useful astools for determining desirable operational bounds for oxide-removalprocesses. As known in the art, oxide removal depends on variousfactors, including but not limited to, oxide-removal processtemperature, process atmosphere, and process time. As an exemplary useas a process improvement tool, standards are formed of the same basematerial with similarly structured slots as a turbine component ofinterest. The nature and extent of oxidation is essentially identicalbetween the standards. A standard is subjected to an oxide cleaning rununder a first set of process conditions. A second run using a secondstandard is made varying at least one process condition. Subsequent runsusing other standards vary other process conditions. Oxide removalamounts and other parameters for each of the runs are determined. Anenhanced combination of oxide-removal process conditions, for example anenhanced oxide-removal amount.

[0034] An exemplary method of forming a standard will now be discussed.This method is merely exemplary and not meant to limit the invention inany way. A first step in the preparation of a standard involves using awire electro-discharge machine (WEDM) to form slots in the standard. Thestructure and operation of standard WEDMs are known by those of ordinaryskill in the art, and thus a detailed description is not provided. Thestandard is then etched and degreased to remove a recast layertherefrom.

[0035] The standard is then compressed, if needed. The compressionoccurs in a press that comprises tungsten carbide platens. The standardis oriented in the press to apply a force in the direction of arrows 10(FIGS. 1 and 4). The standard is compressed with a suitable force toform crack-like defects. When the applied force is removed, and the slotreopens slightly due to elastic unloading of the material. Thestandard's slots are now reduced in thickness t to less that about 50%of the original thickness. For example, if 0.10 mm wire is used to makea simulated defect in the form of a slot having a thickness of about0.12 mm, the simulated defect slot defect may be compressed to less thanabout 0.05 mm.

[0036] The solution heat treatment of the standard comprises placing thestandards on an alumina tray, so the slot structures are out of contactwith the tray and adjacent standards do not touch. The tray is thenplaced into an air furnace. The temperature in the furnace is increasedto about 1250° C. at a rate of about 25° C./min and held for about 1hour to solution the material. The standards are next oxidized at atemperature of about 1150° C. for about 300 hours. Thereafter, thefurnace is cooled to a temperature below about 100° C. at a ratesufficient to form dense oxides in the simulated defects.

[0037] While various embodiments are described herein, it will beappreciated from the specification that various combinations ofelements, variations or improvements therein may be made by thoseskilled in the art, and are within the scope of the invention.

We claim:
 1. An article of manufacture comprising: a block of material,the block being made of a material upon which an oxide can form; and adefect structure disposed in the block of material, wherein an oxidizedarticle is capable of being used to determine parameters of an oxideremoval process by measuring oxide removal from the block and defectstructure after the oxide removal process.
 2. An article according toclaim 1, wherein the block of material comprises a nickel-, cobalt-, oriron-nickel-based superalloys, or combinations thereof.
 3. An articleaccording to claim 1, wherein the block of material comprises agenerally rectangular solid block of material.
 4. An article accordingto claim 3, wherein the defect structure comprises at least one slotdisposed in the block of material.
 5. An article according to claim 1,wherein the defect structure comprises at least one slot that isdisposed in faces of the block of material.
 6. An article according toclaim 5, wherein the at least one slot comprising a thickness in a rangefrom about 10 micrometers (μm) to about 1 millimeter (mm ) and a depthin a range from about 10 micrometers to about 10 millimeters.
 7. Anarticle according to claim 6, wherein the at least one slot comprisesslots on a plurality of faces of the block.
 8. An article according toclaim 1, wherein the standard further comprises a notch disposed in theblock of material.
 9. An article according to claim 8, wherein the notchcomprises a “V” notch in the block of material.
 10. An article accordingto claim 1, wherein the slot comprising a constant thickness in a rangefrom about 10 μm to about 2 mm and a depth in a range from about 10micrometers to about 10 millimeters, the “V” notch and the slot beingseparated by a bridge of material.
 11. A tool for determining oxideremoval parameters of an oxide removal process, the tool comprising: ablock of material, the block being formed of a material upon which anoxide can be formed; and a defect structure disposed in the block ofmaterial, wherein an oxidized tool is capable of being used to determineparameters of an oxide removal process by measuring oxide removal fromthe block and defect structure after the oxide removal process.
 12. Atool according to claim 11, wherein the block of material comprises anickel-, cobalt-, or iron-nickel-based superalloys, or combinationsthereof
 13. A tool according to claim 11, wherein the block of materialcomprises a generally rectangular solid block of material.
 14. A toolaccording to claim 11, wherein the defect structure comprises at leastone defect disposed in the generally rectangular solid block.
 15. A toolaccording to claim 11, wherein the defect structure comprises slots thatare disposed in opposed faces of the generally defect solid block ofmaterial.
 16. A tool according to claim 15, wherein the at least oneslot comprising a constant thickness in a range from about 10micrometers (μm) to about 1 millimeter (mm) and a depth in a range fromabout 10 micrometers to about 10 millimeters.
 17. A tool according toclaim 16, wherein the at least one slot comprises opposed slots, eachopposed slots comprising a constant thickness in a range from about 10micrometers (μm) to about 1 millimeter (mm).
 18. A tool according toclaim 11, wherein the standard further comprises a notch in the block ofmaterial.
 19. An article according to claim 11, wherein the notchcomprises a “V” notch in the block of material.
 20. A tool according toclaim 19, wherein the “V” notch and the at least one slot are separatedby a bridge of material.
 21. A tool according to claim 11, whereindefect structure comprises an oxide-filled, crack-like defect, and theoxide removal parameters comprise at least one of: depth of oxideremoval in the crack-like defect and the surfaces of the generallyrectangular solid block of material, braze repair capability, depth ofbraze filing, and alloying element depletion at the crack-like defectand surfaces of the block of material.
 22. A tool according to claim 21,wherein the oxide removal process parameters are determined by anevaluation comprising at least one of: optical inspection, brazingevaluation, weight loss measurement, electrical resistivity measurement,and wetability evaluation.
 23. A tool according to claim 11, wherein thetool determine benchmarks for the oxide removal process.
 24. A toolaccording to claim 23, wherein the benchmarks comprise at least one of:oxide removal amounts as a function of process time; oxide removalamounts as a function of reactor temperature; oxide removal as afunction of reactor design and loading configuration; alloying elementdepletion of the block of material; alloying element depletion of theblock of material as a function the oxide removal process; efficiency ofthe individual reactor; oxide removal as a function of the process run,and oxide removal as a function of previous oxide removal processes. 25.A process of determining oxide removal status, the process comprising:disposing an oxidized standard in a reactor, the reactor capable ofimplementing an oxide removal process, the oxidized standard comprisinga block of material, the block being formed of a material upon which theoxide is formed and a defect structure disposed in the block ofmaterial; conducting an oxide removal process; and evaluating thestandard for at least one of oxide removal amounts as a function ofprocess time; oxide removal amounts as a function of reactortemperature; oxide removal as a function of reactor design and loadingconfiguration; alloying element depletion of the block of material;alloying element depletion of the block of material as a function theoxide removal process; efficiency of the individual reactor; oxideremoval as a function of the process run, and oxide removal as afunction of previous oxide removal processes.
 26. A process according toclaim 25, wherein the slot structure comprises a simulated crack-likedefect and the step of evaluating comprises exposing the simulatedcrack-like defect.
 27. A process according to claim 26, wherein thestandard comprises the simulated crack-like defect and a notch opposedto the simulated crack-like defect, the step of exposing the simulatedcrack-like defect comprises: compressing the standard at the notch toexpose surfaces of the simulated crack-like defect.
 28. A processaccording to claim 25, wherein the step of evaluating comprises:exposing the simulated crack-like defect by metallographicallysectioning the standard and splitting the standard at a simulatedcrack-like defect.
 29. A process according to claim 25, wherein the stepof evaluating comprises: evaluating by optical inspecting, brazingcapability determination, electrical resistivity measuring, weight lossmeasuring, and wetability evaluating.
 30. A process according to claim25, wherein the process of determining oxide removal status furthercomprises determining at least one of: oxide removal amounts as afunction of process time; oxide removal amounts as a function of reactortemperature; oxide removal as a function of reactor design and loadingconfiguration; alloying element depletion of the block of material;alloying element depletion of the block of material as a function theoxide removal process; efficiency of the individual reactor; oxideremoval as a function of the process run, and oxide removal as afunction of previous oxide removal processes.
 31. A process for formingan oxide removal process evaluation standard, the standard comprising ablock of material, the block being formed of a material upon which anoxide can be formed; and a simulated defect structure disposed in theblock of material, wherein the standard is capable of determining oxideremoval process status, the process comprising: machining the simulateddefect structure in the block of material; and exposing the block ofmaterial to a thermal treatment to form an oxide on the block ofmaterial and on surfaces of the simulated defect structure.
 32. Aprocess according to claim 31, wherein the step of exposing the block ofmaterial to a thermal treatment comprises controllably exposing theblock of material to a high-temperature, oxidizing thermal environmentfor time period to form oxides on the block and filling the simulateddefect structure.
 33. A process according to claim 31, furthercomprising compressing the simulated defect structure to form asimulated crack-like defect after the step of machining the simulateddefect structure.